$DE01/56833/RR+1: Extended Control-Register
On read:
+-------+--------------------------------------------------------+
| Bit 7 | ROM bank selector (A15) |
| Bit 6 | 1 = REU compatible memory map active |
| Bit 5 | ROM bank selector (A16) |
| Bit 4 | ROM bank selector (A14) |
| Bit 3 | ROM bank selector (A13) |
| Bit 2 | 1 = Freeze button pressed |
| Bit 1 | AllowBank bit (see Write) |
| Bit 0 | 1 = Flashmode active (jumper set) |
+-------+--------------------------------------------------------+
On write:
+-------+--------------------------------------------------------+
| Bit 7 | ROM bank selector (A15) - mirror of $DE00 |
| Bit 6 | 1 = REU compatible memory map |
| Bit 5 | ROM bank selector (A16) - only in Flashmode |
| Bit 4 | ROM bank selector (A14) - mirror of $DE00 |
| Bit 3 | ROM bank selector (A13) - mirror of $DE00 |
| Bit 2 | 1 = disables Freeze function |
| Bit 1 | AllowBank bit (1 = allows banking of RAM in |
| | $DE02/$DF00 areas) |
| Bit 0 | 1 = enable accessory connector (SilverSurfer) |
+-------+--------------------------------------------------------+
If not in Flash mode: Bits 1, 2, 6 can only be written once.
Bit 5 is always 0.
If in Flash mode: Bit 6 cannot be set.
Register will not be disabled by the first write.